Denary number to roman numerals (golang)

Use Google's modern Go language (aka. golang) to convert a denary number (base 10) to a roman numeral. Just a good exercise to explore Go's map, slice, sort and for loop features.

Note that in Go the := is shorthand for assigning a type (by inference) and a value to a variable. A slice is like an array that can grow, and a map is a key indexed list. Go has only the for loop, but the syntax is very flexible and can accomplish all the usual loop duties.